It works in the free market because there's a force ready to beat the crap out of anyone who steals, murders, destroys or otherwise does something centrally detrimental to the free market. You can't participate in a free market well if someone just waltzes off with whatever you're marketing, or just shoots you and dumps your remains behind a grocery store dumpster.
"People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf."
- George Orwell
(Shall the "rough men" be hired only by those who can afford their services, or hired for all by general taxation?)